Thermodynamic Analysis of a Reverse Osmosis Desalination System Using Forward Osmosis for Energy Recovery

Thermodynamic analysis is applied to assess the energy efficiency of hybrid desalination cycles that are driven by simultaneous mixed inputs, including heat, electrical work, and chemical energy. A seawater desalination cycle using work and a chemical input stream is analyzed using seawater properties. Two system models, a reversible separator and an irreversible component based model, are developed to find the least work required to operate the system with and without osmotic recovery. The component based model represents a proposed desalination system which uses a reverse osmosis membrane for solute separation, a pressure exchanger for recovering a fraction of the flow work associated with the pressurized discharge brine, and a forward osmosis (FO) module for recovering some of the chemical energy contained within the concentrated discharge brine. The energy attained by the addition of the chemical input stream serves to lower the amount of electrical work required for operation. For this analysis, a wastewater stream of varying solute concentration, ranging from feed to brackish water salinity, is considered as the chemical stream. Unlike other models available in the literature, the FO exchanger is numerically simulated as a mass exchanger of given size which accounts for changing stream concentration, and consequently, stream-wise variations of osmotic pressure throughout the length of the unit. A parametric study is performed on the models by varying input conditions. For the reversible case it is found that significant work reductions can be made through the use of an energy recovery device when the inlet wastewater salinity used is less than the feed salinity of 35 g/kg. For the irreversible case with a typical recovery ratio and feed salinity, significant work reductions were only noted for a wastewater inlet of less than half of the feed salinity due to pump work losses. In the irreversible case, the use of a numerical model to simulate the FO exchanger resulted in a maximum work reduction when the pressure difference between streams was around one half of the osmotic pressure difference as opposed to the precise value of one half found in zero-dimensional exchanger models.Center for Clean Water and Clean Energy at MIT and KFUPM (Project R4-CW-08

Effectiveness-mass transfer units (ε-MTU) model of a reverse osmosis membrane mass exchanger

A strong analogy exists between heat exchangers and osmotic mass exchangers. The effectiveness-number of transfer units (ε-NTU) method is well-known for the sizing and rating of heat exchangers. A similar method, called the effectiveness-mass transfer units (ε-MTU) method, is developed for reverse osmosis (RO) mass exchangers. Governing equations for an RO mass exchanger are nondimensionalized assuming ideal membrane characteristics and a linearized form of the osmotic pressure function for seawater. A closed form solution is found which relates three dimensionless groups: the number of mass transfer units, which is an effective size of the exchanger; a pressure ratio, which relates osmotic and hydraulic pressures; and the recovery ratio, which is the ratio of permeate to inlet feed flow rates. A novel performance parameter, the effectiveness of an RO exchanger, is defined as a ratio of the recovery ratio to the maximum recovery ratio. A one-dimensional numerical model is developed to correct for the effects of feed-side external concentration polarization and nonlinearities in osmotic pressure as a function of salinity. A comparison of model results to experimental data found in the literature resulted in an average error of less than 7.8%. The analytical ε-MTU model can be used for design or performance evaluation of RO membrane mass exchangers.Center for Clean Water and Clean Energy at MIT and KFUPMNational Science Foundation (U.S.). Graduate Research Fellowship (Grant 1122374

Osmotic mass exchangers for power generation and energy recovery : analysis and analogy to heat exchangers

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 151-156).Desalination is an important separation process which can provide water scarce regions with clean water for drinking or for agricultural use. Thermal distillation has historically been the dominant method for obtaining pure water, but today, reverse osmosis (RO) produces a greater percentage of the total desalinated water worldwide by a large margin. Fundamentally, an RO system is a membrane-based osmotic mass exchanger. Another type of membrane-based osmotic process, a subset of forward osmosis (FO) called pressure retarded osmosis (PRO), currently exhibits promise for making desalination more energy efficient and is receiving attention in the literature. PRO exchangers are capable of producing power from two streams of different salinity and recovering energy from the brine stream of any desalination process when paired with water pumps and turbines. RO and PRO exchangers are essentially mass exchangers with a hydraulic or osmotic pressure difference across a membrane acting as the predominant driving potential. Using a simple resistance model for mass transfer applied across an ideal RO and PRO membrane, closed form expressions are developed which relate the performance of a one-dimensional membrane as a function of membrane properties, membrane area, inlet salinities, operating conditions, and flow configuration. These closed form expressions are analogous to the effectiveness versus number of transfer unit (c-NTU) models which have been used for decades in the rating and sizing of heat exchangers. The closed form expressions, along with numerical simulations for validating the models, are used to determine the limits of permeate flux in one-dimensional RO, PRO, and FO membranes; analyze the power performance of a one-dimensional PRO membrane; and determine the viability of using a PRO-based energy recovery device to reduce the net power consumption for RO desalination. The closed-form solutions for determining the performance of the RO and PRO membranes require that osmotic pressure be defined as a linear function of salinity. It is found that for a seawater RO process with a typical recovery ratio of 50% or less, the maximum error associated with linearization is less than 6.1%. For brackish water desalination, where processes typically operate at very high recovery ratios but have brine salinities lower than those encountered in seawater desalination, the error does not exceed 1.8%. For PRO membranes, using varying linearization curves, maximum errors for flux performance of less than 5.5% are incurred by the linear approximation. It is also found that the maximum Second Law efficiency of the power achievable from a one-dimensional PRO membrane is 66.48%. For large membrane areas, the maximum power for a PRO membrane occurs at a hydraulic pressure difference that is not equal to exactly one-half the osmotic pressure difference as reported in literature for zero-dimensional PRO membranes. For PRO membranes used for brine chemical energy recovery from an RO plant treating a feed stream of 35 g/kg, it is found that a wastewater salinity of less than 20 g/kg is required to recover power. Because the membranes within this study have been assumed as ideal, the performance results for flux, power, and power recovery can serve as informative upper bounds.by Leonardo David Banchik.S.M

On the present and future economic viability of stand-alone pressure-retarded osmosis

Pressure-retarded osmosis is a renewable method of power production from salinity gradients which has generated significant academic and commercial interest but, to date, has not been successfully implemented on a large scale. In this work, we investigate lower bound cost scenarios for power generation with PRO to evaluate its economic viability. We build a comprehensive economic model for PRO with assumptions that minimize the cost of power production, thereby conclusively identifying the operating conditions that are not economically viable. With the current state-of-the art PRO membranes, we estimate the minimum levelized cost of electricity for PRO of US$1.2/kWh for seawater and river water pairing,$0.44/kWh for reverse osmosis brine and wastewater, and $0.066/kWh for nearly saturated water (26$0.074/kWh. We show two methods for reducing this cost via economies of scale and reducing the membrane structural parameter. We find that the latter method reduces the levelized cost of electricity significantly more than increasing the membrane permeability coefficient.National Science Foundation (U.S.) (Graduate Research Fellowship Program, Grant No.1122374) )Kuwait Foundation for the Advancement of Sciences (KFAS) (Project No. P31475EC01

Fortaleciendo las habilidades matemáticas de los alumnos ingresantes desde los entornos virtuales

La práctica académica docente y la implementación de aplicaciones tecnológicas innovadoras llevadas a cabo durante los últimos años en la educación universitaria basada en el paradigma de la educación a distancia, nos instan a afirmar que los alumnos dedican un tiempo insuficiente tanto para el trabajo autónomo como para la revisión de sus propias estrategias de aprendizaje; que los conceptos y habilidades aprendidos durante los cursos de matemática son olvidados al poco tiempo y que es muy baja la solidez de lo asimilado. El crecimiento exponencial de la información, la masificación que va adquiriendo el acceso a los medios y recursos tecnológicos y lo cambiante de estas tecnologías, unido al impacto cada vez mayor de las potencialidades computacionales señalan la necesidad de formas sistémicas e integradoras del conocimiento soportadas por un pensamiento flexible y basado en estrategias cognitivas y metacognitivas de aplicación en amplias expresiones del saber. Nuestro interés está centrado en la identificación de las habilidades cognitivas que traen, adquieren o están presentes en los pensamientos matemáticos de los alumnos de educación a distancia en carreras de pregrado o en los procesos de articulación disciplinar para el ingreso a la universidad

Hydride precipitation and stresses in zircaloy-4 observed by synchrotron X-ray diffraction

The grain stresses within hydrides precipitated in rolled zircaloy-4 plates were determined by synchrotron X-ray diffraction experiments using an 80 keV photon beam and a high-speed area detector placed in transmission geometry. Results showed large compressive stresses (360 ± 20 MPa) in the hydrides along the plate rolling direction. The origin of these stresses was investigated by performing hydride dissolution/precipitation in situ for thermal cycles between room temperature and 400 C. A large stress hysteresis was observed, with a steady decrease on heating and an abrupt change on cooling. The observed stresses are explained by the constraint imposed by grain boundaries on the growth of hydride platelets on the rolling–transverse plane of the rolled plates.Fil: Santisteban, Javier Roberto. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Vicente Alvarez, Miguel Angel. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Vizcaino, Pablo. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Banchik, A. D.. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Almer, J. D.. No especifíca

Effect of crystallite orientation and external stress on hydride precipitation and dissolution in Zr2.5%Nb

Thermal cycling of Zr2.5%Nb pressure tubes specimens containing ∼100 wt ppm H between room temperature and 400 °C produces the dissolution and re-precipitation of zirconium hydride, with a distinctive hysteresis between these two processes. In this work, we have found that the details of the precipitation and dissolution depend on the actual orientation of the α-Zr grains where hydride precipitation takes place. In situ synchrotron X-ray diffraction experiments during such thermal cycles have provided information about hydride precipitation specific to the two most important groups of α-Zr phase orientations, namely crystallites having c-axes parallel (mHoop) and tilted by ∼20° (mTilted) from the tube hoop direction. The results indicate that hydrides precipitate at slightly higher temperatures (∼5 °C), and dissolve at consistently higher temperatures (∼15 °C) in mTilted grains than in mHoop grains. Moreover, application of a tensile stress along the tube hoop direction results in two noticeable effects in hydride precipitation. Firstly, it shifts hydride precipitation towards higher temperatures, at a rate of ∼(0.08 ± 0.02) °C/MPa for hydrides precipitated in the mHoop grains. Secondly, it produces a redistribution of hydrogen between grains of different orientations, increasing hydride precipitation on those α-Zr grains having their c-axes stretched by the external load. A detailed analysis of the diffracted signal shows that such redistribution occurs during the precipitation stage, as a result of changes in the precipitation temperatures for different grain orientations.Fil: Vizcaino, Pablo. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Santisteban, Javier Roberto. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Vicente Alvarez, Miguel Angel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Banchik, Abraham David. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Almer, J.. Argonne National Laboratory; Estados Unido

Energy consumption in desalinating produced water from shale oil and gas extraction

On-site treatment and reuse is an increasingly preferred option for produced water management in unconventional oil and gas extraction. This paper analyzes and compares the energetics of several desalination technologies at the high salinities and diverse compositions commonly encountered in produced water from shale formations to guide technology selection and to inform further system development. Produced water properties are modeled using Pitzer's equations, and emphasis is placed on how these properties drive differences in system thermodynamics at salinities significantly above the oceanic range. Models of mechanical vapor compression, multi-effect distillation, forward osmosis, humidification–dehumidification, membrane distillation, and a hypothetical high pressure reverse osmosis system show that for a fixed brine salinity, evaporative system energetics tend to be less sensitive to changes in feed salinity. Consequently, second law efficiencies of evaporative systems tend to be higher when treating typical produced waters to near-saturation than when treating seawater. In addition, if realized for high-salinity produced waters, reverse osmosis has the potential to achieve very high efficiencies. The results suggest a different energetic paradigm in comparing membrane and evaporative systems for high salinity wastewater treatment than has been commonly accepted for lower salinity water.Center for Clean Water and Clean Energy at MIT and KFUPM (Project R4-CW-08)Center for Clean Water and Clean Energy at MIT and KFUPM (Project R13-CW-10)National Science Foundation (U.S.). Graduate Research Fellowship (Grant 1122374)Masdar Institute of Science and Technology (Massachusetts Institute of Technology Cooperative Agreement 02/MI/MI/CP/11/07633/GEN/G/00

Crises Press Coverage: Local & Foreign Reporting on the Arab-Israel Conflict

This study analyzes Israeli Haaretz and the American New York Times crisis press coverage on four short Arab-Israel crises, from the early 1950s to the late 1990s. To illuminate the similar and different reporting modes of the press from within and outside a conflict region, the article probes three hypotheses: reporting on the salient crisis events will differ (H1), reporting on conflict related events will differ (H2) and dominant media functions will differ (H3). Findings on most reporting variables examined in both newspapers support these hypotheses. Compared with the NYT, in Haaretz, overall crisis exposure was higher, crisis was addressed more frequently than conflict, use of pictures was negligible and surveillance substituted correlation. But in both papers, similar peaks and lulls were reported for all four short Arab-Israel crises, coverage of crisis was the overwhelming topic and surveillance was the dominant media function

An evaluation of membrane properties and process characteristics of a scaled-up pressure retarded osmosis (PRO) process

YesThis work presents a systematic evaluation of the membrane and process characteristics of a scaled-up pressure retarded osmosis (PRO). In order to meet pre-defined membrane economic viability ( ≥ 5 W/m2), different operating conditions and design parameters are studied with respect to the increase of the process scale, including the initial flow rates of the draw and feed solution, operating pressure, membrane permeability-selectivity, structural parameter, and the efficiency of the high-pressure pump (HP), energy recovery device (ERD) and hydro-turbine (HT). The numerical results indicate that the performance of the scaled-up PRO process is significantly dependent on the dimensionless flow rate. Furthermore, with the increase of the specific membrane scale, the accumulated solute leakage becomes important. The membrane to achieve the optimal performance moves to the low permeability in order to mitigate the reverse solute permeation. Additionally, the counter-current flow scheme is capable to increase the process performance with a higher permeable and less selectable membrane compared to the co-current flow scheme. Finally, the inefficiencies of the process components move the optimal APD occurring at a higher dimensionless flow rate to reduce the energy losses in the pressurization and at a higher specific membrane scale to increase energy generation